Indole derivatives and pharmaceutically acceptable salts thereof are disclosed in WO 2012/128689 and WO 2014/046589 in form of mixtures of cis/trans isomers (Z/E isomers) at the N-methylidene entity. These compounds are useful in the treatment of solid cancers. The anti-cancer effect is believed to be based on the iron-chelating property of the compounds. Since the rate of isomerization at physiological conditions seemed to be substantial it was presumed that the pharmacological effect of the isomers was substantially similar or even the same.
Eshba et al., discloses N-(1-pyridine-2-yl-methylidene)-N-(9H-1,3,4,9-tetraza-fluoren-2-yl)-hydrazine derivatives as antiviral and anti-cancer agents, wherein only one compound show cytotoxic activity. It is desirable for a pharmaceutical composition to be well-defined, in particular of its pharmacologically active constituents. It is therefore essential that if a compound exists in two isoforms, the more active isomer of said compounds has to be dominant in the pharmaceutical composition thereof. In addition, a pharmaceutical composition should be sufficiently stable allowing it to be stored for an extended period of time without noticeable change of its constitution.
New and effective anticancer drugs need to be developed for patients that suffer from cancer. Drug development over all is associated with a lot of difficulties until a final product is reached. Initially a promising compound is identified and experimentally tested in different in vitro models, and after that preclinical studies are initiated most often by the use of different mouse models. Until this point, only small amounts of the compound need to be synthesized, and the purity requirements are lower than those required in clinical studies conducted in humans. There are many steps in drug development that are critical, e.g., identifying and isolating the active compound, investigating whether a particular isomer is more potent than the other, further have a permissible degree of purity, stability, and also that said compound can be manufactured in large scale. These are not trivial steps and many promising compounds/drugs fail to reach the market due to manufacturing problems as described above.